DNS study on viscoelastic effect in drag-reduced turbulent channel flow

Abstract

The effect of viscoelastic contribution on wall-bounded turbulent flow of drag-reducing surfactant solution is investigated through direct numerical simulations (DNS). A series of DNS on turbulent channel flow is performed for different rheological properties at two different Reynolds numbers. It is found that high drag reduction is achieved by suppressing the turbulent contribution for the high Weissenberg number, and/or by decreasing the viscosity ratio and the effective viscosity. A highly drag-reduced turbulent flow at a high Reynolds number is mainly caused by the viscoelastic effect in the elastic layer, whereas the outer layer flow hardly affects the drag reduction. Moreover, we focus on the viscoelastic contribution term in the budget of Reynolds stress and its relation to the local flow pattern. It is shown that in the near-wall region of the highly drag-reduced flow a positive work done by viscoelastic stress is closely associated with vortex stretching that produces turbulent kinetic energy from stored elastic energy, whereas a negative one causes vortex compression.

Keywords:

• Non-Newtonian fluid
• direct numerical simulation
• drag reduction
• turbulent channel flow
• topological classification

Acknowledgements

The present computations were performed using supercomputing resources at the Cyberscience Center at Tohoku University. This work was conducted in the Research Center for Holistic Computational Science (Holcs). The third author (B.Y.) expresses appreciation for the support of the National Science Foundation of China (Nos. 50876114, 50506017, and 10602043), SRF for ROCS, SEM Specialised Research Fund for the Doctoral Programme of Higher Education of China (No. 20050425006), and the Key Project of the Chinese Ministry of Education (No. 106034).